Can't beat Notepad for clean and simple. I hand-code everything.
I've got TextPad on hand for validation errors and spell checking. I suppose that I could use it exclusively, but have always coded in Notepad. I do run final product through TextPad for spell checking.
Been doing it long enough that validation is mostly just a double-check. Not many errors to be found. However, if I didn't close a <div> on line 300, TextPad has line number option, so I use it.
My version of TextPad is probably five years old, so probably even better now. There are a lot of good hand-coding editors available with handy 'bells and whistles', but that don't mess with your code as with WYSIWYG. That is, they do what they are told (or allowed) and nothing more - just like a good text editor should.